1. Field of the Invention
The invention relates to the heat treating of glassware and crystalware articles in a plane perpendicular to an axis of rotation and to a device implementing such a method.
2. Description of the Prior Art
The purpose of the heat treatment of glassware or crystalware articles in a plane perpendicular to an axis of rotation is generally to introduce transient mechanical stresses into the material making up the article, which is generally fragile, or to bring a part or the whole of the material making up the article, which material is situated in proximity to this plane, to within the plastic range.
An operation involving the action of transient stresses is called demoiling. In this case, the stresses are intended to cause or to propagate fissures, designated as thermal fissures, the purpose of which is to separate from the article per se the mass of glass or crystal, hereinafter referred to as moil, which served to retain the article in the course of its phase of shaping by hot plastic deformation. The demoiling per se is generally preceded by a scribing operation, the purpose of which is to create at the surface of the fragile material making up the article, in the desired plane for the separation of the moil, hereinafter referred to as the demoiling plane, by the action of a blunt tool, a mechanical fissure which is generally resulting from earlier operations and to round off the edge of the article in such a manner as to make its use more pleasant.
The heat treatment of glassware or crystalware articles in a plane perpendicular to an axis of rotation is conventionally performed with the aid of a source of heat or of cold, for example one or more burners conventionally utilized, one or more laser beams, one or more infrared radiant sources, or any other type of appropriate heat or cold generators, judiciously disposed within the environment of the article, in such a manner as to induce within this article an adequate temperature field. The articles are conventionally caused to execute a rotational movement about the axis of rotation under consideration in such a manner that the temperature field is as similar as possible within each section of the article passing through this axis. The treatment is performed either at a single working station or at a plurality of working stations by periodic indexing, or in a continuous and progressive manner by a heat or cold source disposed in a rectilinear or curvilinear float; in this latter case, the articles to be treated pass along in front of this float at an appropriate speed and the position of the heat or cold source constituted by the float in relation to the article is defined in a conventional manner by the projection of the configuration in a plane perpendicular to the relative movement of the article in relation to the float.
The relative position of the heat or cold source in relation to the articles is conventionally regulable for each type of article, and in particular the relative position of the heat or cold source in relation to the articles in a plane passing through the axis of rotation of the article in the course of treatment. The inclination of the heat or cold source in relation to the axis or rotation of the article, especially if the source is highly directional, is also of importance and is conventionally regulable for each type of article.
The practice of the heat treatment of glassware or crystalware articles in a plane perpendicular to an axis of rotation shows that, in the majority of cases, the best result is obtained when the distance between the heat or cold source and the wall of the article to be treated is kept constant. The practice of the heat treatment utilizing the flame burner or any other highly directional heat source likewise shows that, in the majority of cases, the best result is obtained when the direction of the flame or more generally of the heat flux, in a plane including the axis of rotation of the article, is perpendicular to the wall of the article.
In current practice, the heat or cold source being positioned in relation to the article to be treated, either manually or by a more sophisticated automatic system, only for one type of article, without taking account of the disparities from article to article or of particular geometries linked to the type of article, it follows that the optimal conditions are realized during the entire treatment of a particular article only where the latter is round and if its axis of symmetry rigorously coincides with its axis of rotation.
Now, it is known from practical considerations that, although the articles of one and the same type are clearly similar, they are not rigorously identical. The dimensional difference is defined as the geometric defect between a real article and its ideal model. The articles constructed by means of automatic part-forming machines generally exhibit geometric defects of a few tenths of a millimeter, while the articles manufactured by craftsmen may exhibit geometric defects which are far larger, in the order of few millimeters; cases are also known in which it becomes necessary to treat articles, the cross section of which is intentionally not round, but is presented in the form of a regular polygon or of any other regular or irregular shape.
The variation of the distance between the heat or cold source and the wall of the article to be treated, from one article to another or, for one and the same article, during the rotation of the latter in front of the heat or cold source gives rise to variations of the temperature field in various sections of the article passing through its axis of rotation, Furthermore, in the practice of the heat treatment utilizing as heat source the flame burner or any other highly directional source, in the case where the heat source is inclined in relation to the axis of rotation of the article, a variation of the distance between the wall of the article and the heat source gives rise to a proportional displacement of the point of intersection of the wall and of the heat flux in relation to the selected treatment plane; this fact is highly detrimental and, in the case of demoiling, gives rise to irregular fractures which condemn the article or necessitate, in order to recover the same, lengthy subsequent machining operations.
From French Patent No. 2,164,526, a transfer machine is known, the burners of which are arranged in one or more curvilinear floats which take the exact shape of the displacement path of the articles to be treated, wherein said burners are disposed in the treatment plane and are directed perpendicularly to the external wall of the articles and the curvilinear float(s) are positioned by an ordinary mechanical device and remain fixed while the machine is working without manual intervention of any operator.
From U.S. Pat. No. 2,704,418 it is known also a machine with a single working station comprising several burners arranged in a circle in regard to the axis of the mandrel bearing the article. Said burners are inclined in relation to the treatment plane and their direction makes a small angle with the external wall of the article, in this document too, the position of the burners is manually regulated and remains unchanged throughout the entire duration of the treatment.
French Patent No. 1,136,999 discloses a transfer machine for cutting off glass tubes. This machine comprises at least one marking-off station and a heating station. On the marking-off station, the edge-tool is elastically maintained against the external wall of the tube. The heating station comprises a sole burner arranged in the plane of treatment and is disposed tangentially in relation to the wall. In this document, the burner is mounted on a carrier connected to by means of a mechanism to a path which is elastically maintained in contact with the external wall of the tube, wherein the displacement of the contact path in function of the concentricity disparities or ovalization disparities controlling the displacement of the burner, in such manner that the flame remains tangential in regard to the tube.
Hence, the following up of a heat source is a function of disparities from a particular article. In this case, only the tangential direction of the burner is maintained unchanged while the distance in relation to the action point on the external wall may fluctuate in large limits.
The purpose of the present invention is to remedy to the drawbacks described alone.